XML 109 R97.htm IDEA: XBRL DOCUMENT v3.6.0.2
Employee Benefit Plans (Retiree Medical Coverage) - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]    
Maximum number of years medical, dental and prescription drug coverage to spouse of deceased officer 30 years  
Total liability recorded to provide medical, dental and prescription drug coverage $ 0.2 $ 0.2